The highest praise one could grant it was "not as bad as those other bad Bug-types." Outshining the likes of Butterfree, Beautifly, and Dustox could hardly be called a talent, and Venomoth's decidedly mediocre stats and typing left it as a forgettable Pokemon despite its impressive movepool and abilities

Mothim:
Mothim is another forgotten Bug / Flying-type Pokemon, and for a good reason: he has a crippling 4x weakness to Stealth Rock, making him almost unviable on a competitive team. This, coupled with his paper-thin defenses and several common weaknesses, means that Mothim won't stay alive for very long. He is also slow and easy to revenge kill. It can also be said that Mothim is outclassed by Venomoth, who is faster.

Butterfree:
Butterfree has finally become a Pokemon worthy of use. With BW's gifts to her in the forms of Tinted Lens and Quiver Dance, Butterfree has found a comfortable place in the NU metagame as the most lethal Quiver Dance sweeper available. The picturesque combination of Sleep Powder, Quiver Dance, and Tinted Lens makes for a lethal combination in NU, and Butterfree's stats are just good enough to utilize these moves perfectly.

Beautifly:
Notably, BW gave Beautifly a huge buff in the form of Quiver Dance, which, despite being an excellent boosting move, was sadly also given to almost every other Bug-type in NU. Beautifly sports an outstanding special movepool coming off of a base 90 Special Attack, which is pretty much the only good thing going for it.

Dustox:
Notably nothing to say but it has a very poor movepool and can be taken out by any Pokemon.

SO,I would say venomoth comes first,followed by butterfree,beautifly and dustox.Mothim is the weakest.

Venomoth wins, as it has a decent sweeping movepool, as well as access to Baton Pass and Sleep Powder.

Ranking:
1. Venomoth. Not only can it sweep with Quiver Dance, it also has Baton Pass, allowing it to create monsters.
2. Butterfree. It has both decent SAtk and access to Sleep Powder, facilitating its sweep.
3. Beautifly. It does have access to a large range of coverage moves, but will often need to resort to Focus Sash for longevity. Also has good SAtk and okay Speed.
4. Mothim. It has good SAtk and lame Speed, but it outclasses Dustox in both.
5. Dustox. This guy sucks. Poor Speed and SAtk, and can get revenged easily due to its poor Speed.